Description.
Circuit shown here can be used to jam FM radios in its vicinity. The circuit is nothing but a classic single transistor oscillator operating in the VHF region. Working principle of the circuit is very simple and straight forward. Powerful VHF oscillations from the circuit will interfere with the FM signals to nullify it. Jammer circuits like this are illegal in many countries and you must assemble this circuit on your own responsibility. This circuit is intended only for fun and i request you not to misuse it.Circuit diagram.

Notes.

For L1 make 6 turns of 16AWG enamelled copper wire on a 9mm plastic former.

The circuit can be powered using a 9V PP3 battery.

For extended range, use an antenna.

A 30cm long wire connected anywhere on the coil will do for the antenna.

thing one. where should I connect a probe to measure voltage by oscilloscope? It seems that a frequency depend on where i put the probe. the prove even detects the signal when it is detached from a circuit.
thing two. even if there is no C and L in tank circuit except wires, the circuit makes oscillation like 200Mhz is it normal?

Please see the notes for details.
Hi Rex you can use shortest lead possible for all components in the oscillator stage. Try to wax them such that the winding and the frequency tuned circuit does not vibrate. Connect external antenna to the first turn from the supply end such that antenna should not load the tank circuit heavily. Use regulated supply with proper decoupling.

I built it and it works like a charm! To increase power I have to change the 2N2222 with a 2N2219 and replace the power source with a 12V one? And regarding the power, in a few words, how can I calculate the emitted power?
One last thing. What is the role of C2?

Without C2 the circuit will not oscillate. You cannot calculate easily like total DC power supplied to the circuit divided by 2 or 3. as it requires many parameters to be calculated, you require like VSWR meter etc.

I’d like to ask something about the capacitors. C4 is an electrolytic (polarized) capacitor and it must be installed the proper way, but what about C3 and C2? Can they be ceramic (without any concern for polarization)? Also, I couldn’t find a 6pF for C2. Is 6.8pF OK?

ok, I built this on breadboard and it works. I just used a coil a made about a month ago for another schema – 16AWG 100 turns on 20 mm diameter plastic tube. How you do the coil doesn’t seem to matter much because you set the frequency from the capacitor.

Hi, if I calculate the values for L and C in order for this circuit to jam frequencies in SHF (GHz) will it do it or do I have to change some other component? Can the transistor sustain a frequency of say 3GHz?

Seetharaman, this jammer circuit will work, but will face one problem, the human body capacitance will damped the oscillation in the tank circuit and it can affect the frequency stability.. How do i connect crystal to stabilise the frequency.. Please help me

if you connect a crystal to the circuit then what ever the crystals frequency is then that is the only frequency that you will be able to jam using this circuit. iF you actually want to still connect a crystal then use a 100MHz on because with the inductor being a coil than the tolerance to the crystal changes to about 97MHz-103MHz (jamming those frequencies only)(tolerance=3%)
where to connect (using schematic): joint north of 6 pF cap. then add 10 ohm (1% or it will screw up the oscillation) resistor on top of it then crystal then connect other end of crystal to coil. the wire joint that comes from south of trimm cap. and goes right connects to the joint between the crystal and the coil in the situation that i have just described

Guys I just put this together and IT WORKS !!! I used the exact same parts as listed in this schematic minus the transistor. The substitute I used for the 2N2222 transistor was the BC337, you can find that one commonly. Also instead of a 6pF cap I used a 5.6pF and it still works. You have to pay attention to the trimmer capacitor and turn it using an insulated/non-conductive tool (you can put a plastic bag between the cap and a screwdriver and it´ll still work). The inductor doesn´t have to be super accurate either. The tuning is super sensitive so you have to get used to that too, it takes some time. The trimmer capacitor doesn´t have to be the exact same one, it should just cover its range in terms of capacitance. Hope I cleared some of your questions out … Cheers

Hi Adi the component list you can make a list from the circuit and the notes. As for the function is concerned it is just an oscillator producing a blank carrier, which will beat with the transmitted signal and the demodulated signal at the receiver will not have any audible information except some beating signal.

please need help! i couldnt find 16 awg wire.i m having 4 awg.can some tell to make inductor of 4 awg wire??????????As i hav selected it as my semster project i will have to make presentation in few days!!!!!

hey, can i have the list of components with all the power rating and stuff…i want to make this for my college project….so i would like to have the list of all the componnts with all the specifications ASAP

heya, thanks alot for the link man, helped out alot, i apreciate the help you’ve given. would it be alright to use the ceramic variable caps they sell also, i’m planning on making a pcb and size matters lol, plus the capacitance more closely matches your design 🙂 also, could this schematic be used with some few tweaks to jam all sorts of frequencies, like cell or AM or anything else?

Alright, thanks for the help, i apreciate it alot, now, i’m just wondering where to get the variable cap, i’ve found out all the different names and corps that manufacture them, but so far all the places i’ve been to haven’t seen or heard of them in about five years 🙁 online is the same, i’ve so far found one site but its over in england, 🙁 and sites or tips you have would be great to circumnavigate this issue, (eg. something else i could use, a site, etc.)

Hi Jem it is common ground, that is earth plane of your antenna. If you donot want earth plane you can leave it and use only the wavelength / 4 whip antenna.
I have not tried simulation but tried the circuit and it is working alright.

ok thank you, now just one more question, i know what all the components are in this, but i’m having trouble translating in my brain how they all connect, i know it should be all easy because of the blueprint, but like, does the second path coming down south off the 9volt source, is that just another positive, or is that the ground coming back to the batter? and if so why the ground symbol on the bottom, is is a common ground for all the components?

hey, i’m trying to build one of these, and i was wondering, do the components have to be rated for 9 volts? cuz i’m looking for one of those variable trimmer caps and all i’m finding are ones that have a working voltage of 100 🙁

Hi Bryce what capacitor value you have used for C2. It can be upto 10PF ceramic disc, L1 should be 6 to 9mm dia air core with 18SWG super enameled copper wire close wound 5 to 6 turns. set the trimmer C1 at the center.
once the circuit is assembled keep it close to an FM radio tuned to around 100MHz. now switch on the jammer, with a plastic tool expand the coil axially till a blank carrier is heard in the radio. now your FM radio jammer is ready.

Hi Bryce by reducing emitter resistance and providing heat sink to 2N2222 and increasing the supply to 12volt you can achieve your requirement. you can replace 2N2222 with 2N2219 for better power desipation

[…] Notes. For L1 make 6 turns of 16AWG enamelled copper wire on a 9mm plastic former.The circuit can be powered using a 9V PP3 battery.For extended range, use an antenna.A 30cm long wire connected anywhere on the coil will do for the antenna.For better performance, assemble the circuit on a good PCB. Link – circuitstoday […]

The legality of the circuit depends on how and where you use it. It is basically a CW generator so a radio will just pick up silence. It differs little from the little transmitters that allow a CD player to be picked up on a nearby radio. There’s just no input where a mic or CD player could be attached. In most jurisdictions, the limiting factor is SWR. So if it can only be picked up for a few meters, the legality would depend on how you use it. If you’re only interfering with your own radio, it should be alright in most places. If you’re intentionally interfering with other peoples’ radios, then it’s illegal almost everywhere.